The De la Torre Elementary principal first heard accusations of sexual misconduct a decade before the instructor's arrest this week, the L.A. schools chief says.

A now-retired principal twice failed to report accusations of sexual misconduct by a teacher who this week was charged with molesting 12 students at a Wilmington elementary school, officials said.

In 2002 and 2008, the principal was told that the teacher, Robert Pimentel, 57, inappropriately touched a student. But the principal failed to tell law enforcement authorities, as required by law, said L.A. schools Supt. John Deasy.

The Los Angeles Police Department began investigating Pimentel only last March, when they learned of more recent allegations at George de la Torre Jr. Elementary School.

LAPD Capt. Fabian Lizarraga said Thursday that detectives will launch an investigation into whether the principal, Irene Hinojosa, should face charges for failing to report alleged abuse. She could not be reached for comment Thursday.

It remains unclear why Hinojosa did not tell authorities about the accusations. The 2008 allegation also occurred at De la Torre, where she was principal. The 2002 allegation was made when Pimentel was a teacher and Hinojosa the principal at Dominguez Elementary in Carson, Deasy said.

At De la Torre, volunteer Magdalena Gonzalez said Thursday that Hinojosa had been made aware of several questionable incidents involving Pimentel.

Three years ago, she said, a girl told her parent that Pimentel had playfully spanked students. Gonzalez also said she and other volunteers saw Pimentel pull on a student's bra strap during a fifth-grade graduation ceremony.

Gonzalez alleged that Hinojosa was dismissive of their complaints and that she allowed Pimentel to have students in his classroom during recess and lunch despite their misgivings.

"We told her he was touching the girls," Gonzalez said in Spanish.

School employees are required by law to report allegations of sexual misconduct to police. They also are supposed to report such issues to their supervisors, according to school district policies.

The revelations angered parents and once again placed the Los Angeles Unified School District under scrutiny over its handling of student-abuse cases. A state audit released last November found that Los Angeles school officials failed to promptly report nearly 150 cases of suspected misconduct to state authorities, including allegations of sexual contact with students.

The audit resulted from the furor over the case of a Miramonte Elementary School teacher who last year was accused of spoon-feeding his semen to blindfolded students, giving them tainted cookies and taking bizarre photos of them. The school had received previous complaints about the teacher, Mark Berndt, that had resulted in no discipline. Berndt has pleaded not guilty to lewd conduct.

On Thursday, Deasy criticized the handling of the De la Torre case by the state Commission on Teacher Credentialing. He said the district informed the state of the allegations as soon as they came to light, but the commission has not suspended or revoked the credential of either educator.

If Pimentel had applied to work as a substitute teacher at another school system, for example, the state would have reported him in good standing as recently as Thursday.

A spokeswoman said the commission cannot automatically suspend a teacher's credential until charges are filed. But the commission does have the discretion to act sooner, said Erin Sullivan, who said state law prevents her from commenting on specific cases.

Hinojosa's case is "scheduled to be taken up by the commission" next Thursday at its regular meeting, she added.

Pimentel is charged with seven counts of lewd and lascivious acts on children under 14 and with eight felony counts of continuous sexual abuse involving eight victims. The charges cover the period from September 2011 to March 2012, when Pimentel worked at De la Torre. He was charged with molesting 12 students, but police allege there is a total of 20 child victims and one adult victim.

Pimentel was taken into custody shortly after noon Wednesday and was being held on $12 million bail. He pleaded not guilty Thursday, and his attorney Richard Knickerbocker said he is "absolutely innocent."

Knickerbocker described the touching as appropriate and said it fell within district policy.

In one instance, Pimentel hugged a girl and "gave her a kiss on the forehead," Knickerbocker said. Pimentel, he said, never touched "any private parts."

"Right now, we have accusations," Knickerbocker said. "That's all."

Prosecutors did not detail Pimentel's alleged crimes in court papers.

But a law enforcement source close to the investigation said he has been accused of touching children "multiple times over a period of time."

The source, who spoke on the condition of anonymity because the case was ongoing, said Pimentel is accused of inappropriately touching 9- and 10-year-old girls, sometimes under their clothing and in their genital areas.